Like cuckoos, honeyguides are parasitic birds that lay their eggs in other birds’ nests and dupe them into raising their young. Now scientists reveal that, unlike in cuckoos, the resemblance between honeyguide eggs and those of their bee-eater bird hosts hasn’t evolved to trick hosts into accepting the imposter egg as one of their own. Rather, it appears to have evolved to trick other honeyguides who would otherwise destroy the eggs because of fierce competition for host nests. The new research is published today, 21 August, in the journal Biology Letters.
Honeyguides are intriguingly odd birds that are best-known for their unique, mutually beneficial relationship with humans. Honeyguides love to eat beeswax. To obtain it, they guide human honey-hunters to bees’ nests. In return for showing the humans the bees, the honeyguide gains access to the otherwise dangerous and impenetrable nest and its sought-after wax.
But these African birds also have a dark side. They are unusually vicious parasites whose imposter chicks stab the chicks of their host birds (often little bee-eaters) to death as soon as they hatch in order to eliminate competition for the host parents’ care. The newly published research has shown that this fight for monopoly of the nest also extends to other honeyguides in a battle conducted deep underground in the nest burrows that bee-eaters dig into the roofs of Aardvark holes.
The researchers’ curiosity was piqued by their earlier finding that like cuckoo eggs, honeyguide eggs resemble those of each of their several host species. Instead of mimicking their colour, however, they mimic their size (as colour is irrelevant in the dark interior of the deep holes in which hosts breed). For example, honeyguides parasitising little bee-eaters lay smaller eggs in their nests than do honeyguides parasitising larger hosts. Many classic studies have shown that comparable mimicry in cuckoo eggs has evolved to reduce rejection by choosy hosts that eject mismatched eggs from their nests.
Read more at: Phys.org